1. Field of the Invention
The present invention relates to a dielectric filter, a dielectric duplexer, and a transceiver.
2. Description of the Related Art
Recently, a small, light in weight, and thin-type of radio communication equipment such as a mobile phone have been rapidly popular. In addition to this tendency, electronic components which are to be mounted on such a type of radio communication equipment are required to have a small size and a reduced height. Furthermore, a dielectric duplexer, which is an antenna-shared unit for performing reception and transmission by a single antenna, is required to be small-sized, lightweight, and lower in height.
Conventionally, a dielectric duplexer used as an antenna-shared unit in a mobile phone or the like adopts a structure in which resonator holes of a plurality of dielectric resonators are aligned in a straight line in a single dielectric block. However, generally, both a filter on the transmitting side and a filter on the receiving side, which are composed of dielectric resonators formed on the dielectric block, are allowed to block a pass band of the counter-side filter by band-pass filter characteristics, so that it is difficult to obtain sufficient attenuation in an attenuation band, as long as the number of the dielectric resonators is not increased. Thus, the dielectric duplexer having a structure in which the resonator holes are aligned in a straight line, needs to be large overall.
As a result, it is considerable, for example, that the transmitting filter may be formed by a band-block filter. When a single dielectric block is used, a transmission-line conductor is disposed for coupling adjacent resonators by setting a phase difference of .pi./2 (rad) between them. In this case, since the transmission line is a microstrip line whose half-face is dielectric and its other half-face is air, the electrical length of the line is longer than the resonator length of the dielectric resonator, so that the dimension of the aligning direction of the resonators is very large.
In addition, for example, even though the transmitting filter is used as a band-block filter in the case of an antenna-shared unit, when the transmitting filter side is viewed from the side of the receiving filter, in the pass band of the receiving filter, namely, in the block band of the transmitting filter, impedance is substantially zero, so that receiving signals from the antenna flow to the side of the transmitting filter. In order to avoid such a situation, it is necessary to dispose a phase unit having the electrical length of .pi./2 between the transmitting filter and an antenna terminal so as to make the impedance in the block band of the transmitting filter viewed from the side of the receiving filter infinite. However, this arrangement increases the number of components in the radio communication equipment, thereby leading to rising in cost.
In order to solve the above-mentioned problems in the conventional dielectric duplexer, for example, a duplexer shown in FIGS. 9A to 9C is presented. The duplexer comprises rectangular-parallelepiped formed dielectric block 1, and with respect to it, various holes, and an electrode film are formed. In other words, 2a, 2b, 2c, 5a, 5b, and 5c are resonator holes on the side of the transmitting filter of the dielectric duplexer; and 4a, 4b, 4c, and 4d are resonator holes on the side of the receiving filter. Numeral reference 3 is an input-output coupling resonator hole.
Each of the respective resonator holes 2a through 5c is a step hole whose internal diameters of the upper half part and the lower half part in FIG. 9B mutually differ. In order not to make the figure complicated, resonator holes 5b and 5c are not shown in FIG. 9B. In this figure, 12a, 12b, and 12c are inner conductors formed on the inner wall surfaces of the resonator holes 2a, 2b, and 2c; 15a is an inner conductor formed on the inner wall surface of the resonator hole 5a; 14a, 14b, 14c, and 14d are inner conductors formed on the inner wall surfaces of the resonator holes 4a, 4b, 4c, and 4d; and 13 is an inner conductor formed on the inner wall surface of the input-output coupling resonator hole 3.
In addition, in each of the inner conductors except for the inner conductors 12a and 13, a nonconductive portion indicated by g is disposed near the extremity of a step hole having a longer internal diameter so as to use this part as a disconnection end. Holes 6a, 6b, and 6c shown in FIG. 9A are ground holes, in which inner conductors are formed on the entire inner peripheral surfaces of the straight holes with fixed internal diameters. On the external surface of the dielectric block 1 are formed a transmitting terminal Tx and an antenna terminal ANT, respectively connecting to the inner conductors 12a and 13 of the resonator holes 2a and 3; and a receiving terminal Rx is formed to make capacitance between it and the inner conductor 14d of the resonator hole 4d. Furthermore, an outer conductor 10 is formed on the substantially entire surface except for these terminals Tx, Rx, and ANT.
Meanwhile, in the dielectric duplexer having the aforementioned structure, as shown in FIGS. 9A to 9C, since the resonator holes 2a through 2c, 3, 5a through 5c and the ground holes 6a through 6c of the dielectric resonators comprising a filter on the transmitting side are aligned in a staggering form in the dielectric block 1, the dimension w of the aligning direction of the resonator holes 2a through 2c is reduced, whereas the height h is increased when it is mounted on a print circuit board, or the like. In addition, in the conventional dielectric duplexer, arrangement of the resonator holes 2a through 2c and the ground holes 6a through 6c are complicated, and also it is difficult to form and manufacture the dielectric block 1.
Furthermore, in the dielectric duplexer shown in FIG. 9, only Q.sub.0 characteristics of approximately 2/3 is obtainable as compared with the one having the same height as that in which the resonator holes are aligned in a line in the dielectric block; and when the height h is reduced, the characteristics are deteriorated.